N. Emami | Search arXiv

arXiv2022

The Origin of the Observed Lyman alpha EW Distribution of Dwarf Galaxies at z~2

We present a rest-UV selected sample of 32 lensed galaxies at $z\sim 2$ observed with joint Keck/LRIS rest-UV and Keck/MOSFIRE rest-optical spectra behind the clusters Abell 1689, MACS J0717, and MACS J1149. The sample pushes towards the faintest UV luminosities observed ($-19 \le {\rm M_{\rm UV}} \le -17$) at this redshift. The fraction of dwarf galaxies identified as Ly$\alpha$ emitters ($\rm EW \ge 20\ \overset{\lower.5em\circ}{\mathrm{A}}$) is ${\rm X_{\rm LAE}}=25^{+15}_{-10}\%$. We use the Balmer lines and UV continuum to estimate the intrinsic EW allowing us to distinguish the effects of the ionizing spectra and Ly$\alpha$ escape fraction on the observed EW distribution. Fainter galaxies ($\rm M_{\rm UV} > -19$) show larger intrinsic EWs and escape fractions than brighter galaxies. Only galaxies with intrinsic EWs greater than 40$\ \overset{\lower.5em\circ}{\mathrm{A}}$ have escape fractions larger than 0.05. We find an anti-correlation between the escape fraction and $\rm A_V$ as well as UV spectral slope. The volumetric escape fraction of our sample is $f_{\rm esc}^{\rm Ly\alpha} = 4.59^{+2.0}_{-1.4}\%$ in agreement with measurements found elsewhere in the literature. About half of the total integrated Ly$\alpha$ luminosity density comes from galaxies with ${\rm EW}_{\rm obs}>20\ \overset{\lower.5em\circ}{\mathrm{A}}$.

astro-ph.GA↗

arXiv2022

Observations of the luminous red nova AT 2021biy in the nearby galaxy NGC 4631

We present an observational study of the luminous red nova (LRN) AT\,2021biy in the nearby galaxy NGC\,4631. The field of the object was routinely imaged during the pre-eruptive stage by synoptic surveys, but the transient was detected only at a few epochs from $\sim 231$\,days before maximum brightness. The LRN outburst was monitored with unprecedented cadence both photometrically and spectroscopically. AT\,2021biy shows a short-duration blue peak, with a bolometric luminosity of $\sim 1.6 \times 10^{41}$\,erg\,s$^{-1}$, followed by the longest plateau among LRNe to date, with a duration of 210\,days. A late-time hump in the light curve was also observed, possibly produced by a shell-shell collision. AT\,2021biy exhibits the typical spectral evolution of LRNe. Early-time spectra are characterised by a blue continuum and prominent H emission lines. Then, the continuum becomes redder, resembling that of a K-type star with a forest of metal absorption lines during the plateau phase. Finally, late-time spectra show a very red continuum ($T_{\mathrm{BB}} \approx 2050$ K) with molecular features (e.g., TiO) resembling those of M-type stars. Spectropolarimetric analysis indicates that AT\,2021biy has local dust properties similar to those of V838\,Mon in the Milky Way Galaxy. Inspection of archival {\it Hubble Space Telescope} data taken on 2003 August 3 reveals a $\sim 20$\,\msun\ progenitor candidate with log\,$(L/{\rm L}_{\odot}) = 5.0$\,dex and $T_{\rm{eff}} = 5900$\,K at solar metallicity. The above luminosity and colour match those of a luminous yellow supergiant. Most likely, this source is a close binary, with a 17--24\,\msun\ primary component.

astro-ph.SR↗